High brightness laser diode source

ABSTRACT

Coherent light sources combining a semiconductor optical source with a light diverging region, such as a flared resonator type laser diode or flared amplifier type MOPA, with a single lens adapted to correct the astigmatism of the light beam emitted from the source is disclosed. The lens has an acircular cylindrical or toroidal first surface and an aspheric or binary diffractive second surface. The first surface has a curvature chosen to substantially equalize the lateral and transverse divergences of the astigmatic beam. Sources with an array of light diverging regions producing an array of astigmatic beams and a single astigmatism-correcting lens array aligned with the beams are also disclosed. The single beam source can be used in systems with frequency converting nonlinear optics. The array source can be stacked with other arrays to produce very high output powers with high brightness.

TECHNICAL FIELD

The present invention relates to optical systems forming a coherentlight source of high power and brightness, and in particular to suchsources that include a high brightness, semiconductor laser diode, suchas a single-spatial-mode broad-area laser diode, a flared-resonator-type(unstable resonator) laser diode or a MOPA device, in combination withastigmatism-correcting optics for that source.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,321,718, Waarts et al. describe a coherent light sourcehaving an astigmatism-correcting lens system positioned in the path of ahigh power, but astigmatic, coherent light beam from a semiconductoroptical source such as a flared-amplifier-type MOPA device or aflared-resonator-type laser diode. A number of lens configurations aredescribed, which include combinations of cylindrical and spherical lenssurfaces. While most of the embodiments use from two to four lenses, oneembodiment employs a single lens with two crossed positive cylinder lenssurfaces. Another embodiment uses a lens having a positive toric surfaceand a planar surface. All of the lens systems are adapted to provide amodified astigmatism-free light beam from the astigmatic light receivedfrom the semiconductor optical source. The astigmatism-free light isuseful for many laser applications, including frequency conversion, ofwhich a number of configurations are disclosed.

In U.S. Pat. No. 5,369,661, Yamaguchi et al. disclose an optical systemfor coupling light from a semiconductor laser array into a solid-statelaser medium or into an optical fiber. The optics include a gradientindex (GRIN) lens array to condense the individual light beams emittedwith a large divergence angle from the semiconductor laser array to formparallel collimated light beams. A separate aspherical lens thenconverges the light beams into a single beam spot. Stacks of two or morelaser arrays with corresponding stacks of two or more GRIN lens arraysare also disclosed, which form a 2-D array of parallel light beams. Anaspherical lens then condenses the array of light beams to a beam spotfor coupling to a fiber. Plural sets of stacked arrays may be combinedby arranging their respective optical fibers to form a fiber bundle.

U.S. Pat. Nos. 5,229,883 to Jackson et al., 5,081,639 to Snyder et al.,and 5,293,269 to Burkhart et al. disclose lens optics for collimatingthe diverging light output from diode lasers and diode laser arrays.Jackson et al. use a first cylindrical lens for collimating the light inthe fast axis (or transverse direction) and a second binary diffractiveoptical element or array of such elements, simulating one or moreaspheric lens surfaces, for collimating the light in the slow axis (orlateral direction). Snyder et al. use a cylindrical lens having anelliptical or hyperbolic cross-section, while Burkhart et al. use a lenswith a circular-cylindrical back surface and an acircular-cylindricalfront surface. Both of these cylindrical lenses are formed by means of afiber lens drawing process from a master or preform having the desiredcross-section.

In U.S. Pat. No. 5,216,687, Fujino et al. employ a spherical first lensor a GRIN lens array for collimating the light from a semiconductorlaser or laser array in the fast axis, and a bicylindrical second lenswith crossed (orthogonally oriented) cylindrical surfaces for focusingthe light in both its fast and slow axes to a spot.

In providing lens optics for semiconductor laser sources that emithighly astigmatic light beams, such as flared-resonator-type laserdiodes or flared-amplifier-type MOPAS, it is desirable that the opticsnot only correct for the astigmatism in the light, but also be compact,have a minimum number of refracting surfaces within the constraints ofmanufacturability, be easily positioned in front of the laser source atthe proper locations within the design tolerances, and preferably beinexpensive to make. A minimum loss of brightness is preferred, so thatnumerical aperture is an important design parameter. Likewise, whenarrays of such astigmatic laser sources are used, the corresponding lensarrays need to provide a precise center-to-center spacing betweenlenslets and be designed, if possible, for maximum beam filling of theemitted array of light beams. Unfortunately, many of these requirementsconflict so that trade-offs must be made. A theoretical designcalculated from purely optical considerations may include lens surfaceswhich are difficult and very expensive to manufacture. If the design islimited to easily manufactured lenses with circular-cylindrical andspherical lens surfaces, multiple lenses are required, which must beprecisely positioned, and which generally limit the numerical apertureand beam filling factor that are achievable, thus reducing brightness.

An object of the invention is to provide a coherent light source inwhich the astigmatism-correcting lens optics for high powersemiconductor laser sources that emit astigmatic light beams preservethe brightness of the emitted light, while being compact, inexpensivelymanufacturable and easily positioned for astigmatism-correction and beamcollimation.

Another object of the invention is to provide an astigmatism-correctinglens array for a diode laser array that is inexpensive to manufacturewith maximum beam filling and brightness conservation of the array ofemitted beams.

SUMMARY OF THE INVENTION

The objects of the invention are met with a coherent light sourcecomprising a semiconductor optical source generating and emitting a highpower coherent light beam that is astigmatic, and a singleastigmatism-correcting lens positioned in the path of the light beam,where this single lens has a first acircular-cylindrical or toroidallens surface and a second aspheric or binary diffractive lens surface.The objects are also met with a coherent light source comprising asemiconductor optical source generating and emitting an array of highpower coherent light beams, each of which is astigmatic, and a singleastigmatism-correcting lens array positioned in the paths of the lightbeams, such that each lenslet is aligned with a corresponding laserlight emitter of the source, and where a first surface of the lens arrayis either an acircular cylinder extending across the width of the arrayor an array of toroidal lens surfaces aligned with the light beams. Thesecond lens array surface is an array of either aspheric or binary lenselements.

The toroidal surfaces of these lenses or lens arrays can be made easilyand inexpensively with a mold, in which either the mold itself or amaster for the mold is machined using a technique that involves cuttingwith a diamond-tipped cutting tool into the circumferential surface of acylindrical blank mounted on a rotating spindle. The depth of the cutvaries axially to create a toroidal surface or an array of toroidalsurfaces whose axial cross-section can be acircular. The section cutperpendicular to the master's rotation axis is necessarily circular.When the mold itself is machined in this way, the toroidal surfaceformed by the diamond turning technique is a negative of the resultingtoroidal lens surface. When the machined surface is used as a master tocreate the mold, the original toroidal surface of the master can be apositive of the final lens surface created by the mold.

The semiconductor optical source that is combined with the singleastigmatism-correcting lens may be included in an optical cavity havinga gain region with a lateral dimension along its length in the cavitythat is greater than a lateral dimension of the light path along otherportions of the optical cavity. For example, it can be aflared-amplifier-type MOPA device, a flared-resonator-type (unstableresonator) laser diode, or some other laser diode with a light divergingregion therein. Alternatively, it may be a wide-area laser diode with anangled DFB grating or any other spatially coherent source with strongastigmatism.

The coherent light sources with their astigmatism-correctedlaser-diode-based emission can be used in a number of applicationsrequiring high power astigmatism-free beams. For example, the source canbe coupled to a frequency-converting nonlinear optical medium.Alternatively, multiple laser source/correction lens systems can bestacked to form a 2-D array, then coupled by focusing optics into anoptical fiber to create a very high power source. Such a light sourcecan be employed, for example, in a system for material processing, suchas material cutting, welding or surface treatment with the light beam.Other applications for these sources are also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are respective lateral and transverse sections takenthrough the optical axis of a coherent light source of the presentinvention with a cylindrical-aspherical lens.

FIGS. 3 and 4 are respective lateral and transverse sections takenthrough the optical axis of a coherent light source of the presentinvention with a toroidal-aspherical lens.

FIGS. 5 and 6 are perspective views illustrating cutting of a master ormold for a toroidal lens surface and a toroidal lens array surfacerespectively.

FIG. 7 is a perspective view of a coherent light source of the presentinvention including a semi-conductor laser array and a lens array with atoroidal lens array surface formed with the mold in FIG. 6.

FIG. 8 is a top plan view of a coherent light source of the presentinvention including a cylindrical-binary lens array.

FIG. 9 is a side view showing the coherent light source of FIG. 8stacked upon another like light source.

FIG. 10 is a perspective view of a stacked laser system with a pluralityof coherent light sources like those illustrated in FIGS. 8 and 9.

FIG. 11 is a perspective view of the stacked laser system of FIG. 10coupled by focusing optics to an optical fiber to form a high powerlaser-fiber unit.

FIG. 12 is a perspective view showing a plurality of high powerlaser-fiber units of FIG. 11 combined together into a very high powersystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. 1 and 2, a coherent light source embodying thepresent invention includes (1) a semiconductor optical source 11 whichemits a spatially coherent light beam of high power that is also bothhighly asymmetric and astigmatic, and (2) a single lens 15 with a firstlens surface 17 having an acircular cross-section and a second lenssurface 19, which have curvatures that in combination are adapted tocorrect the astigmatism in the light beam, and which thereby provides amodified astigmatism-free light beam.

The semiconductor optical source 11 may comprise a laser diode with alight diverging region 13 therein. Such a laser diode can be, forexample, a flared-amplifier-type MOPA device or a flared-resonator-typelaser diode (also known as an unstable-resonator (UR) device). In the URdevice, the entire gain region including a flared portion lies withinthe laser cavity, whereas in the MOPA device, at least a portion of aflared gain region lies outside of the laser cavity to form an opticalpower amplifier that is optically coupled to a laser oscillator sectionwithin the laser cavity. Yet another semiconductor optical source 11which could be used may be a wide-area laser diode with a broad gainregion and a distributed feedback (DFB) grating oriented at an angle tothe emitting surface, as taught in U.S. Pat. No. 5,337,328.

All of these semiconductor optical sources 11 produce output laser beamsthat are both highly asymmetric and astigmatic. In the case of the URand flared-amplifier MOPA devices, and other similar laser diodes withlight diverging regions therein, the light propagating in the flaredportion of the device 11 is guided in the transverse direction (definedas perpendicular to the plane of the active gain region 13) as far asthe output facet of the device, but is allowed to diverge in the lateraldirection (defined as parallel to the plane of the active region, andperpendicular to the light propagation direction). One consequence ofthis lateral divergence with transverse guiding is that the lateral beamdimension is at least 10 times and typically several hundred timeslarger than the transverse beam dimension at the emitting surface. Thelateral and transverse divergence angles will usually differ as well,with a typical effective transverse divergence of about 0.35 N.A. (i.e.,about ±20°) and a lateral divergence of about 0.16 N.A. (i.e., about±9°). Moreover, the apparent locations of the lateral and transversebeam waists of the output light do not coincide. The transverse beamwaist is located at or very near to the output facet where transverseguiding ends. The lateral beam waist is located at the narrow end of theflared region, where it is coupled to a single mode waveguide, forexample, and where lateral guiding ends and lateral divergence begins.And although this lateral beam waist is reimaged closer to the outputsurface when the light is refracted as it exits the device, its apparentreimaged location is still a significant distance (usually at least 500μm) behind the transverse beam waist location. In the case of thewide-area angled-DFB laser diodes (also referred to as α-DFB devices),there is also substantial asymmetry due to the broad gain region andvery strong astigmatism since the output beam is nearly collimated inthe lateral direction but diverges very fast in the transversedirection. In all of these cases, the astigmatism in the emitted lightbeam can make such sources unusable for many laser applicationsobtaining an astigmatism-free light beam is critical for mostapplications. The single lens element 15 in FIGS. 1 and 2, or the lens23 in FIGS. 3 and 4, can be used to correct for the astigmatism.

In the particular embodiment shown in FIG. 1, the single lens 15 has aconvex cylindrical first lens surface 17 of acircular cross-section anda radially symmetric, convex aspheric second lens surface 19. Assuming,for example, a typical semiconductor optical source 11 with an effectivetransverse divergence of 0.35 NA, a lateral divergence of 0.16 NA, andan astigmatism of 680 μm of the light beam emitted from its outputsurface, the light beam can be aberration-corrected and focused to around diffraction-limited spot with a divergence of 0.10 NA by a singlelens 15 with the following parameters. The first lens surface 17 ispositioned 475 μm from the output surface of the source 11, and has anacircular cylindrical surface curvature defined by a radius of curvatureof 480 μm, a conic constant of -4.465, and higher order correctionterms. The thickness of the lens 15 is 2000 μm. The second lens surface19 is a rotationally symmetric asphere with a radius of curvature of-864 pm (i.e., a convex surface), a conic constant of -1.182, and higherorder correction terms. The modified astigmatism-free beam is brought toa 0.10 NA, 6 μm diameter focal spot located at a distance of 3660 μmfrom the second lens surface 19.

As seen in the cylindrical-asphere embodiment of FIGS. 1 and 2, the bestresults for the astigmatism-correcting lens 15 are obtained when theconvex cylindrical first lens surface 17 has an acircular (inparticular, hyperbolic) cross-section. However, while these lens couldbe manufactured in quantity by glass molding, it is difficult to producea mold with a concave acircular cylindrical surface. Accordingly, apreferred embodiment, seen in FIGS. 3 and 4, uses a single lens 23 witha toroidal first lens surface 25, instead of the cylindrical lens 15.The second lens surface 27 is a radially symmetric convex asphere, asbefore. Assuming, for example, a typical semiconductor optical source 21with the same output beam characteristics as that from the source 11 inFIGS. 1 and 2, the beam can be aberration-corrected and focused to around diffraction-limited 0.10 N.A., 6 μm diameter spot by single lens23 with the following parameters. The toroidal first lens surface 25 ispositioned 480 μm from the output surface of the source 21, and has atoroidal surface curvature defined by a radius of curvature in thelateral direction of -5.0 mm (i.e., concave) with a lateral conicconstant of zero (i.e., circular lateral cross-section), a radius ofcurvature in the transverse direction of 536 μm (i.e., convex), atransverse conic constant of -6.980, and higher order correction terms.The thickness of the lens 23 is again 2000 μm, and the second surface 27is a convex rotationally symmetric asphere with a radius of curvature of-858 μm, a conic constant of -0.941, and high order correction terms.The focal spot is located at a distance of 3920 μm from the second lenssurface 27.

Both embodiments in FIGS. 1-4 are useful for coupling light into a 0.2N.A., 20 μm core optical fiber. Such a fiber could also be a double-cladfiber with a single-mode core, an inner cladding region surrounding thecore, and an outer cladding surrounding the inner cladding. In suchfiber coupling applications, the aberration correction and beamsymmetrizing provided by the single lens 15 or 23 allows maximum opticalpower and brightness conservation when the light is coupled into thefiber located at or very near to the beam's focal spot. The fibers canbe rare-earth-doped optical fiber amplifiers or lasers, if desired. Thefocused light beam might also be coupled through other single-modeapertures, such as into a frequency doubling waveguide. Instead offocusing the light beam to a spot, the beam could be collimated. Thecoherent light source of the present invention may be located completelywithin a laser cavity, including the single lens, as for example in aresonant doubling configuration, like those described in U.S. Pat. No.5,321,718. Many other applications for the high brightness, high powerastigmatism-free coherent light are possible.

The toroidal-aspheric lenses of the present invention may be made byglass molding processes using a mold that has been cut with adiamond-tipped cutting tool as shown in FIG. 5. The mold begins as acylinder blank 81 mounted axially on a spindle 83. As the spindle 83rotates the blank 81, a diamond tool 85 cuts into the cylindricalsurface 87 to create a negative of the desired lens profile. The radiusof the body 81 determines the radius of curvature in the rotationdirection, while the cutting depth at the various positions of the tool85 along the body's rotation axis on the spindle 81 determines theprofile in the axial direction. It can, therefore, be seen that thesurface profile is necessarily toroidal and that the cross-section ofthe surface taken perpendicular to the rotation axis necessarily has acircular contour. The precise desired acircular shape to be formed inthe axial direction can be computed using available lens designsoftware. Aspheric molds can also be formed using this diamond turningtechnique, but with the cutting tool 85 positioned to remove materialwith a radially symmetric depth profile from the planar top surface ofthe cylindrical blank 81.

Referring to FIG. 6, the same technique can also be used to create aprecise mold for monolithic lens arrays. A cylindrical blank 91 ismounted axially on a spindle 93 and then rotated as a diamond-tippedcutting tool 95 cuts into the cylindrical surface of the blank 91 tocreate the mold for the lens array's toroidal surfaces. The tool 95produces a plurality of identical, adjacent toroidal surface profiles97a, 97b, 97c, . . . , 97n arranged axially along the originallycylindrical surface of the mold 91. The resulting lens 105, seen in FIG.7, has an array of toroidal lens surfaces 107a, 107b, 107c, . . . , 107nwhich can be disposed in front of a monolithic laser diode array or"laser bar" 101 having a plurality of adjacent gain regions 103a, 103b,103c, . . . 103n. The gain regions may include flared or other lightdiverging sections that result in astigmatic light outputs. A separatecylindrical fiber lens 109 may be used to collimate the fast diverginglight in the transverse direction prior to the light encountering theindividual toroidal lens surfaces 107a-107n of the lens 105. The diamondturning technique allows lens arrays to be constructed with very precisecenter-to-center spacing and with high quality precision acircularcross-sections in the transverse direction of each lenslet's surfaceprofile. In addition to cutting concave profiles in the blank 91 seen inFIG. 6, convex profiles could also be cut for a positive master of thelens array. A negative mold would then be formed from the diamond-cutmaster, so that lens arrays with positive curvatures in both transverseand lateral directions can be manufactured.

With reference to FIGS. 8 and 9, a laser diode array 111 having aplurality of laser emitters 113a, . . . , 113i, 113j, . . . , 113noptically coupled to a lens array 115. Both the laser bar 111 and thelens array 115 may be mounted on a common base 114 to maintain alignmentof the corresponding laser emitters 113 and lens array elements 119. Thelaser emitters 113a-n may have a flared other light diverging section,as seen for the emitters 113i and 113j in FIG. 8, such that the lightoutputs are astigmatic. The lens array 115 has a first surface 117 whichis cylindrical in shape to reduce the transverse divergence of theemitted light beams to substantially that of the lateral divergence. Thelens array 115 also has a second surface having a plurality of binarydiffraction lens elements 119a, . . . , 119i, 119j, . . . , 119n. Suchbinary lenslets could be formed by photolithographic etching.Alternatively, molded aspheric lenslets, like the lens surfaces 19 and27 in FIGS. 1-4, could be used in place of the binary lens elements. Ineither case, the lens elements 119a-n collimate the light beams receivedfrom the laser emitters 113a-n. Preferably, the beams are alsosymmetrized at the same time their astigmatism is corrected, and thebeams are allowed to expand to achieve a full (100%) fill factor.Accordingly, the first cylindrical lens surface 117 is positioned wherethe lateral and transverse size dimensions of the beam are substantiallyequal, and the lens array 115 has a thickness such that the lenselements 119a-n are positioned where the adjacent beams substantiallymeet. Beam aspect ratios other than 1:1 are also possible with anappropriate positioning of the first surface 117.

As seen in FIGS. 9 and 10, laser arrays 111, 121, 131, etc. togetherwith their corresponding lens arrays 115, 125, 135, etc. can be stackedone above the other to create an (m×n) matrix of collimated laser beams.Preferably, the stack forms a matrix with a 1:1 aspect ratio. Forexample, a stack of ten laser bars (m=10), each having ten laseremitting elements (n=10), could be formed, where the light from eachemitter 113a-n, 123a-n, etc. is corrected for astigmatism andsymmetrized to a 1:1 lateral-to-transverse beam width ratio by the lenselements 119a-n, 129a-n, etc. of the corresponding stack of lens arrays115, 125, 135, etc. Alternatively, if the light beam from individualbeam elements after astigmatism correction and collimation have adifferent lateral-to-transverse size ratio than 1:1, then the number ofemitters (n) in a laser bar and the number of laser bars (m) in thestack can be chosen so that the stack has a different numerical aspectratio (m:n) than 1:1, such that the overall light output from all of thematrix elements combined has a dimensional aspect ratio of 1:1. As yetanother alternative embodiment, the combined light output from the stackneed not have a symmetric dimensional ratio of 1:1, but could have anydesired degree of asymmetry, if desired.

The stack may be constructed in a manner similar to that described inU.S. Pat. No. 4,716,568 and 5,099,488, or according to any otherwell-known technique used to construct commercially available stackedlaser arrays. As shown in FIG. 10, for example, the laser bars 111, 121,131, etc. may be mounted on plates or blocks 141, 142, 143, etc. ofthermally conductive material. The material may be electricallyinsulative with an electrically conductive surface layer thereon or canbe electrically conductive, such as copper. Typically, the bars 111,121, 131, etc. are mounted p-side down on the plates for efficient heatsinking of the heat generating laser elements. The bases 114, 124, 134,etc. for the lens arrays 115, 125, 135, etc. may be monolithicextensions of the plates 141, 142, 143, etc. for the laser bars 111,121, 131, etc., or may be bonded to the front ends of the plates 141,142, 143, etc., so that the lens arrays 115, 125, 135, etc. are alignedwith their respective laser bars 111, 121, 131, etc. Physical separationbars 112, 122, 132, etc. with a set of spaced apart ribs 139 are alsomounted on each plate 141, 142, 143, etc. These separation bars orstandoffs 112, 122, 132, etc. have a thickness which is approximatelythat of the laser bars 111, 121, 132, etc., so that the ribs 139 extendabove the elevation of each laser bar's top surface such that the laserbars are spaced slightly from the plate 141, 142, etc. above it. Theseparation bars 112, 122, 132, etc. are made of electrically insulativematerial, such as BeO, to isolate their electrically conductive topsurface contact layer from the conductive plate 141, 142, 143, etc. onwhich the bars are mounted. Wire bonds 140 connect the contact layer onthe separation bars 112, 122, 132, etc. to corresponding contact layerson the laser bars 111, 121, 131, etc. The backs of the plates 141, 142,143, etc. are bonded to a thermally conductive but electricallyinsulative backing 145 of a thermal cooler 146 by means of solder 144.The cooler 146 may employ water cooling via inlet and outlet conduits147 and 148 to remove heat from the plates 141, 142, 143, etc.

Referring now to FIG. 11, the collimated light output from the stackedlens arrays 115, 125, 135, etc. can be focused to a spot for couplinginto an optical fiber 157 by means of one or more focusing lenses 151,153 and 155. In addition, if the stack of laser bars 111, 121, etc.provides a light with an aspect ratio of other than 1:1, then thefocusing lenses may include a set of cylinder lenses 151 and 153 toreduce the longer of the lateral or transverse dimension of the lightoutput by an amount necessary to symmetrize the light (e.g., if thestack is 2 cm high by 1 cm wide for a 2:1 aspect ratio of the lightoutput, then a 2:1 reduction in the transverse direction needs to beprovided by the cylinder lenses 151 and 153). The second cylinder lens153 may be a negative lens to recollimate the light. The main focusinglens 155 typically has radially symmetric surfaces, which may be eitherspherical or aspherical in cross-section. A group of several lenselements may combine to form this focusing lens.

In FIG. 12, the cooler, the stack of plates, laser bars and lens arrays,and the focusing optics coupling the astigmatism-corrected light into anoptical fiber 157 form a high brightness laser diode source 161 with atypical output power in the fiber of approximately 100 W. The fiber 157may be a double-clad fiber. A plurality of such units 161, labelled 1,2, 3, . . . , to 10 in FIG. 14, can have their output fibers 157₁, 157₂,157₃, . . . , 157₁₀ formed into a fiber bundle, or combined in a fibercoupler 163 to provide a single high power (1 kW) fiber output 165. Theoptical fiber 165 can also be a double-clad fiber. Other methods of beamcombining, including free-space beam combining, polarization combining,or both, may also be used. The units 161 may be set upon a base 167 witha single water manifold 169 with inlet 171 and outlet 173 providing thecoolant to the water coolers in the respective units. The high powerlaser output from the fiber 165 is useful for material cuttingapplications.

We claim:
 1. A light source comprising:a semiconductor light source forproviding a spatially coherent, astigmatic light beam along a lightpath; a single lens positioned in the light path for receiving the beamhavinga first lens surface for receiving the beam having a firstcurvature that is toroidal with an acircular cross-section and a secondlens surface for exit of the beam having a second curvature that isaspherical.
 2. The light source of claim 1 wherein said semiconductorlight source includes an optical cavity having a gain region with alateral dimension along its length in the optical cavity that is greaterthan a lateral dimension along other portions of the optical cavity. 3.The light source of claim 1 wherein said semiconductor light sourceincludes a light diverging region along the optical path.
 4. The lightsource of claim 1 wherein said light source is employed in a system formaterial processing.
 5. The light source of claim 4 wherein saidprocessing comprises material cutting, welding or surface treatment withthe light beam.
 6. A coherent light source comprising:a semiconductoroptical source generating and emitting at least one high power spatiallycoherent, but astigmatic, light beam from an emitting surface, thesemiconductor optical source characterized by having a large lateralgain width region resulting in highly astigmatic light beam wherein thelateral beam dimension of the light beam at the emitting surface is atleast ten times larger than its transverse dimension at the emittingsurface, a single lens positioned in the path of the light beam emittedfrom the semiconductor optical source emitting surface, the lens havinga first lens surface that is toroidal and a second lens surface that isradially symmetric and aspherical, the first and second lens surfaceshaving curvatures which in combination are adapted to correctastigmatism in said light beam.
 7. The light source of claim 6 whereinsaid semiconductor optical source comprises a laser diode having a lightdiverging region therein.
 8. The light source of claim 7 wherein saidlaser diode is a flared-resonator-type laser diode in which said lightdiverging region is a flared gain region located within a resonant lasercavity of the laser diode.
 9. The light source of claim 7 wherein saidlaser diode is a flared-amplifier-type MOPA device in which said lightdiverging region is a flared power amplifier region optically coupled toa single-mode laser oscillator.
 10. The light source of claim 6 whereinsaid semiconductor optical source comprises a wide-area laser diode witha DFB grating oriented at an angle to an emitting surface thereof. 11.The light source of claim 6 wherein said semiconductor optical sourcecomprises a diode laser array having a plurality of light divergingregions emitting a plurality of high power, coherent, but astigmatic,light beams therefrom, said single astigmatism-correcting lenscomprising a lens array having a plurality of lenslets aligned withcorresponding light diverging regions to receive said plurality of lightbeams.
 12. The light source of claim 11 wherein said first lens surfaceis an array of toroidal lenslet surfaces aligned with said lightdiverging regions of said diode laser array.
 13. The light source ofclaim 11 wherein said second lens surface is an array of radiallysymmetric lenslet surfaces aligned with said light diverging regions ofsaid diode laser array.
 14. The light source of claim 13 wherein saidlenslet surfaces are aspheric surfaces.
 15. The light source of claim 6wherein said first lens surface is positioned where a transversedimension of light emitted from said semiconductor optical source issubstantially equal to a lateral dimension of said light.
 16. The lightsource of claim 6 further comprising an optical fiber optically coupledto the single lens to receive the astigmatism-corrected light beamtherefrom.
 17. The light source of claim 16 wherein said optical fiberis a double-clad fiber.
 18. The coherent light source of claim 6 whereinthe lateral dimension is several 100 times larger than the transversebeam dimension at the emitting surface of the source.
 19. The coherentlight source of claim 18 wherein the apparent reimage location of thelateral dimension is at least about 500 μm within the source from saidemitting surface.
 20. A coherent light source comprising:a semiconductoroptical source generating and emitting a high power spatially coherentlight beam, said source having a light diverging region therein wherebysaid emitted light beam is astigmatic, a single lens having a toroidalfirst lens surface and a radially symmetric, aspherical second lenssurface, said lens positioned in front of said semiconductor opticalsource to receive said astigmatic light beam emitted therefrom, saidfirst and second lens surfaces having orthogonal lateral and transversecurvature components which in combination are selected to correctastigmatism of the light beam.
 21. The light source of claim 20 whereinsaid semiconductor optical source is a flared-resonator-type laserdiode.
 22. The light source of claim 20 wherein said semiconductoroptical source is a flared-amplifier-type MOPA.
 23. The light source ofclaim 20 wherein said semiconductor optical source is a flared amplifierchip, both said chip and said astigmatism-correcting lens being locatedwithin a resonant laser cavity.
 24. The light source of claim 20 whereinsaid semiconductor optical source is a wide-area laser diode with a DFBgrating oriented at an angle to an emitting surface thereof.
 25. Thelight source of claim 20 wherein said first lens surface is positionedwhere a transverse dimension of said light beam emitted from saidsemiconductor optical source is substantially equal to a lateraldimension of said light beam.
 26. The light source of claim 20 furthercomprising an optical fiber optically coupled to the single lens toreceive the astigmatism-corrected light beam therefrom.
 27. The lightsource of claim 26 wherein said optical fiber is a double-clad fiber.28. A coherent light source comprising:a semiconductor optical sourcegenerating and emitting an array of high power spatially coherent lightbeams at an emitting surface, said optical source including a pluralityof light diverging regions arranged side-by-side therein, said lightdiverging regions providing a highly astigmatic light beam wherein thelateral beam dimension of the light beam at the emitting surface is atleast ten times larger than its transverse dimension at the emittingsurface, a single lens array positioned in front of the semiconductoroptical source with lenslets of said lens array aligned withcorresponding light beams emitted from said light diverging regions ofsaid optical source, said single lens array having a first lens surfacethat is toroidal and an array of second lenslet surfaces that areaspherical and radially symmetric and aligned with said light beams,said first lens surface and the array of second lenslet surfaces havingcurvatures which in combination are selected to correct astigmatism ofsaid light beams.
 29. The light source of claim 28 wherein said firstlens surface is an array of toroidal lenslet surfaces aligned with saidlight beams.
 30. The light source of claim 28 wherein said secondlenslet surfaces are positioned where said light beams have expanded tosubstantially fill space between said beams.
 31. The light source ofclaim 28 further comprising at least one optical fiber optically coupledto said lens array to receive the astigmatism-corrected light beamstherefrom.
 32. The light source of claim 31 wherein said at least oneoptical fiber is a double-clad fiber.
 33. A light source comprising:asemiconductor light source for providing a spatially coherent,astigmatic light beam alone a light path; a single lens positioned inthe light path for receiving the beam havinga first lens surface forreceiving the beam having a first curvature that is toroidal with anacircular cross-section, the acircular cross-section beinghyperbolic-shaped and a second lens surface for exit of the beam havinga second curvature that is aspherical.